A new method of producing vaccines to fight polio has emerged, one that does not require the growth of live viruses to manufacture.

Scientists at the University of Leeds in the United Kingdom have successfully produced a virus-free virus-like particle (VLP) vaccine that mimic the “empty” capsids (ECs) normally produced in viral infection, according to findings published in the Journal of Virology.

While vaccines produced from VLPs for hepatitis B and human papilloma viruses have been successful, poliovirus VLPs have previously been too unstable to make practical vaccines.

The research team found a new way to modify VLPS by identifying the mutations that make their structures sufficiently stable to act as vaccines. The empty capsids change shape when warmed and become unusable as vaccines, however the mutations identified in the study prevent those damaging changes.

To produce vaccines using current technologies, an enormous amount of live virus must be produced and then chemically killed, which presents a dangerous security risk of the virus escaping into the environment.

However, a stabilized VLP would eliminate the requirement to grow live viruses.

Poliomyelitis is an infectious disease caused by poliovirus that can result in paralysis and may be fatal.

Polio is caused by three structurally similar but antigenically distinct serotypes of poliovirus termed PV-1, PV-2 and PV-3.

The researchers sought to select PV mutants with increased thermal stability using repeated thermal inactivation followed by passage of surviving virus, focusing on PV-1.

While live-attenuated oral PV vaccines and inactivated-PV vaccines have been used in massive integrated global immunization schemes, there has been major setbacks. OPV has been known to regain virulence through reversion or recombination, which results in individual cases of vaccine-associated paralytic poliomyelitis or polio outbreaks due to circulating vaccine-derived PV.

Although polio has been identified as extinct as a disease and is on the verge of being eradicated world-wide, governments will need to continue to vaccinate to ensure against it recurring. The Leeds research team said the new VLPs would be best used after the virus has been eradicated.

“Continuing to vaccinate after polio has been eradicated is essential to ensure against the disease recurring, but there are significant biosafety concerns about current production methods,” David Rowlands, a professor of Molecular Virology and co-leader of the study, said in a statement.

“Our new method of creating the vaccine has been proven to work in lab conditions and on top of that we’ve proved it’s actually more stable than existing vaccines,” he added. “The improved stability of these modified VLPs means that they can be produced using bioengineering techniques without involving the growth of live virus.”

Further research using rats and mice is planned to ensure that the VLPs are safe and effective for use in humans.

“The international drive to eradicate polio using existing vaccines continues but methods need to be found to maintain vaccination safely as insurance after it appears to have been eradicated,” Nicola Stonehouse, co-leader of the study, from the University of Leeds said in a statement. “This is when our approach will come into its own.

“Further research is needed to refine them more but we are confident they will work for all three forms of polio,” she added. “After that we need to find a way to manufacture them cost effectively on a large scale.”